adapt binary2txt.cpp source to current coding conventions

// Syntax: binary2txt file1 file2 ...

// Creates:           file1.txt file2.txt ...

#include "stdio.h"

#include "string.h"

#include <stdio.h>

#include <string.h>

// these must match settings in src/lmptype.h which builds LAMMPS with

//   -DLAMMPS_SMALLBIG (the default), -DLAMMPS_BIGBIG, or -DLAMMPS_SMALLSMALL